1. Field of the Invention
This invention relates to a control system and a control method for hybrid vehicles having a plurality of prime movers.
The present invention relates to the subject matter contained in Japanese Patent Application No. 2003-160824, filed on Jun. 5, 2003, which is expressly incorporated herein by reference.
2. Description of Related Art
In recent years, there has been proposed a hybrid vehicle on which an engine for outputting a torque by burning fuel and a motor generator for outputting a torque by feeding electric power thereto are mounted, and which is capable of transmitting a torque from the engine and the motor generator to wheels. In the hybrid vehicle of this kind, the fuel economy can be improved and the noise and the exhaust gas emission can be reduced by controlling a driving/halting of the engine and the motor generator on the basis of various conditions.
One example of the hybrid vehicle having a plurality of prime movers as described above is disclosed in Japanese Patent Laid-Open No. 9-117010. In the hybrid vehicle disclosed in Japanese Patent Laid-Open No. 9-117010, an output shaft of the engine is connected to a carrier of a planetary gear unit, and a first counter drive gear is connected to a ring gear of the planetary gear unit. A power is transmitted from the first counter drive gear to a differential unit through a counter driven gear, a pinion gear and the ring gear. Also, said planetary gear unit is connected to a rotor of an electric generator through a sun gear, and is provided with a brake for controlling a rotation/cessation of the rotor. Moreover, there is provided an electric motor to which a second counter drive gear is connected. The second counter drive gear and the counter driven gear are meshing with each other.
According to the hybrid vehicle disclosed in Japanese Patent Laid-Open No. 9-117010, it is possible to switch selectively among three modes such as an engine drive mode, a motor drive mode and an engine/motor drive mode. Under the engine drive mode, first of all, the engine is activated by the electric generator and the electric motor is halted. Under the motor drive mode, the electric motor is driven and the engine is halted. Under the engine/motor drive mode, both the engine and the electric motor are driven together. Namely, according to the hybrid vehicle disclosed in Japanese Patent Laid-Open No. 9-117010, it is possible not only to transmit the torque generated by the engine to the counter driven gear, but also to transmit the torque generated by the electric motor to the counter driven gear. Moreover, according to the hybrid vehicle disclosed in Japanese Patent Laid-Open No. 9-117010, it is possible to lock the rotor of the electric generator by applying the brake. In addition, a technology concerning a hybrid vehicle having a plurality of prime movers is disclosed also in Japanese Patent Laid-Open No. 2002-225578.
However, in the hybrid vehicle disclosed in Japanese Patent Laid-Open No. 9-117010, the second counter drive gear connected to the rotor of the electric motor and the counter driven gear are meshed with each other on a steady basis. As a result, the rotor of the electric motor is rotated by the power of the engine even in the engine drive mode such that only the engine is driven at a high-speed running time, thereby a power loss may become larger.